Continuous molded electrical connector

ABSTRACT

A continuous electrical connector or related part manufactured by injection molding axial segments in sequence. A novel in-line interlocking structure is provided for interlocking adjacent segments. The interlocking structure comprises holed end units nested together with their holes in alignment.

This invention relates to the manufacture of continuous moldedelectrical connectors, and to the resultant strip of electrical headermaterial.

BACKGROUND OF THE INVENTION

Electrical connectors comprising insulating body having electricalcontacts carried thereby are well own in the art. In the so-called malepin connectors, the insulating body carries pin-like contacts whichextend above and below the insulating body to facilitate electricalconnection from one element, such as a printed circuit board (PCB), toanother element, which may, for example, comprise a so-called femaleconnector. As is well known, a female connector comprises an insulatingbody which carries an electrical contact which is generally capable ofreceiving at one end thereof a male pin, and at the other end thereof anelectrical conductor which may be another male pin, a single electricalconductor, or a single strand of a multiconductor flat ribbon cable.Typically, the aforedescribed male connector and female connector areutilized in a tandem or coupled fashion to provide electrical connectionfrom one element such as the printed circuit paths on a PCB toindividual conductors or the multiple conductors of a multiconductorribbon cable.

The aforedescribed male and female type connectors are generallymanufactured with a predetermined number of contacts carried thereby.For example, a typical male connector of the type described above mightcomprise a length of insulating material having two, ten, twenty,thirty, or any number of pins carried thereby. Similarly, a femaleconnector may comprise a body of insulating material having individualcavities disposed therein, each cavity of which carries an electricalcontact. Like the male connectors, the female connectors are commonlymanufactured with two, ten, twenty, thirty, etc., contacts.

There are drawbacks associated with the manufacture and use of both maleand female connectors of the type described above. The end user may useseveral connectors, each having a different number of electricalcontacts or "positions". He must therefore purchase and inventory manydifferent connector sizes, i.e. he must maintain a supply of 8-position,12-position, 20-position connectors, etc.

A continuous connector strip for solving this problem was disclosed inU.S. Pat. No. 4,230,387. U.S. Pat. No. 4,832,622 (the '622 patent),whose contents are herein incorporated by reference, describes a bettersolution to the problem involving continuous extrusion orsemi-continuous injection molding. Problems with the continuousextrusion scheme are that only simple header configurations arepossible, and the extruded strip must in a subsequent step have holespunched and notches formed. While the semi-continuous injection moldingscheme avoids the foregoing problems, it also has drawbacks, which willbe best understood from the following description.

The latter method involves use of an angled protuberance (108) (see FIG.11A of the '622 patent) on the end of a longitudinal spine (106)extending along the strip edge and which serves as the connection devicefor a number of units (102) which are each composed of a discretelymolded segment. After the injection molding and cooling process, eachdiscretely molded segment is removed from the mold cavity and indexedinto a position such that the next discretely molded segment will inturn encapsulate, fuse or overmold the protuberance (108) of theprevious segment. In this method, the protuberance (108) of the previoussegment becomes encapsulated in or fused into the spine (106) andleading end unit (102) of the segment currently being molded. Thisachieves the interlocking of the two discretely molded segments to forma continuous length.

A first drawback with this method is that, the act of removing thediscretely molded segment from the mold and indexing into a positionsuch that the next cycle of the injection mold will encapsulate or fusethe protuberance in exactly the correct position is something that mustbe done with the highest precision, or the two strips will be out ofpitch. Pitch is defined as the distance from one electrical connectiondevice (pin, socket, etc.) to the adjacent one, and is of criticalimportance to the end assembler of the devices, who has to assemble, forexample, a female connector with socket connectors of a given pitch to amale connector with pin connections of the same pitch. This method ofinterlocking the two discretely molded segments relies entirely on therepositioning of the first segment in precisely the correct locationwith relation to the mold cavity that will in turn mold the nextsegment. This is not easy to accomplish in the method described in the'622 patent.

A second drawback of the method presented above is the possibility ofhaving weak joints due to poor materials, poor design, or improperprocessing conditions during the injection molding process. Weak jointswould be subject to breakage, causing the two discretely molded segmentsto separate during the interconnecting device insertion process,shipment or during the end user's assembly process.

SUMMARY OF THE INVENTION

An object of the invention is an improved semi-continuous injectionmolding process for molding a continuous strip of insulating materialwith holes for receiving electrical or mechanical parts.

Another object of the invention is a continuous strip of injectionmolded insulating material provided with holes for receiving electricalor mechanical parts and preferably with severance means, such asnotches, for severing from the strip discrete lengths of the materialfor use, for example, as electrical headers, said strip having been madeby separately molding discrete segments, wherein the discrete segmentsare interconnected by a stronger interlocking structure.

In accordance with one aspect of the present invention, each segment hasa trailing projecting portion, substantially in-line with the strip,with undercuts or recessed regions behind the projecting portion. Theprojecting portion of each previously-molded segment is reinserted inthe mold and the leading portion of the next segment molded over andaround the projecting portion to provide a strong interlocking structuresubstantially in-line with the connector strip.

In a preferred embodiment, the projecting portion has a hole forreceiving an electrical or mechanical part, and the overmolded part alsohas a hole, with both holes aligned to receive the electrical ormechanical part. In this way, despite the fact that the resultantinterlocking structure is in-line in the strip, a space for anelectrical or mechanical part is not lost, so that for an applicationwhere, say, electrical pins are provided in evenly-spaced holes in thestrip, a pin can also be placed in the aligned holes of the interlockingstructure to maintain the symmetry.

These and other objects and attainments together with a fullerunderstanding of the invention will become apparent and appreciated byreferring to the following descriptions and claims taken in conjunctionwith the accompanying drawings which illustrate by way of example andnot limitation preferred embodiments of the invention and wherein likereference numerals denote like or corresponding parts.

SUMMARY OF THE DRAWINGS

In the drawings:

FIGS. 1 and 2 are perspective view of continuous strips of one row andtwo rows, respectively, of pin connectors in accordance with theinvention;

FIG. 3 is a perspective view of one molded segment of a continuousconnector strip as shown in FIG. 1;

FIG. 4 is a perspective view showing how the end regions of adjacentsegments form an interlocking structure according to the invention;

FIGS. 4A and 4B are cross-sections of the structure of FIG. 4 takenalong the lines 4A--4A and 4B--4B, respectively, of FIG. 6;

FIGS. 5 and 6 are plan and elevational views, respectively, of thesegment of FIG. 4;

FIG. 7 illustrates manufacture of a continuous strip according to theinvention;

FIG. 8 illustrate how the user would receive a reeled continuous strip.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The '622 patent illustrates various pin header configurations availablefrom a continuous strip of insulating material with holes filled withcontact elements. FIGS. 1 and 2 illustrate comparable parts availablefrom a continuous strip according to the invention.

The continuous strip 10 comprises, integrally connected, individualunits 12 separated by severance means, in this instance spaced pairs ofnotches 14 between each unit 12 forming weakened regions where the stripcan easily be severed to form one or multiple pin headers. The notchesalso assist in flexing of the strip for later coiling on a reel,provides a convenient reference point for indexing of the strip, anddetermines a specific web size between units 12 to control unit spacing.Each of the units 12 in this case have vertical through-holes 16,beveled 18 at the top or bottom, for receiving straight pin terminals20.

The pins 20 have a substantially square cross section, or alternativelyof a different cross-section, such as round or rectangular, and also mayhave an expanded "star" section in the area covered by the plasticheader for improved strength and for form-fitting with the insulatingplastic to prevent longitudinal displacement of the inserted pins. Thesides of the strip 10 have the notches 14 formed therein, which notchesare substantially U-shaped. The U-shaped notches 14 are directedsubstantially perpendicular to the longitudinal axis of the strip 10. Bysevering the strip at the two opposing notches, an electrical connectorhaving a predetermined number of pin terminals can be formed. In thedescription which follows, the method of the invention will be describedin connection with the manufacture of a single-row connector. However,other connectors, such as those shown in FIG. 2 and in FIGS. 2-4 of the'622 patent, can be manufactured in accordance with the invention.

FIG. 2 is a view of a double-row strip 10' according to the invention,with each unit 12 containing two holes 16 each containing a pin 20, witheach unit 12' separated by pairs of notches 14. In this case, the strip10' is wider than the strip shown in FIG. 1 so that pairs of holes 16can be formed for receiving the two rows of straight pins 20.

The method according to the invention is not limited to the formation ofcontinuous connector strip having straight pin terminals. FIG. 3B of the'622 patent shows an end view of an endless connector having right-anglepin terminals inserted in holes formed in the strip, and FIG. 4B of the'622 patent shows a strip having two rows of right-angle pin terminals.Although the connector strip shown are provided with pin terminals, itis apparent that an electrical connector can be manufactured accordingto the invention having any type of electrical components inserted inthe continuous strip.

FIG. 3 illustrates what is herein termed one segment 22 of thecontinuous strip, which is made up of a plurality of such segments 22interlocked or fused together. Each segment 22 is constituted of aplurality of units 12, and includes end units comprised of a leading endunit 24 and a trailing end unit 26 (explained below), each with theapproximately same sized hole 16 as the middle units 12 between the endunits 24, 26.

A feature of the invention is the use of the end units 24, 26 ofadjacent segments 22 to form a strong interlocking structure connectingthe discretely molded segments 22 into a continuous strip 10. This isaccomplished with an improved style of interlocking feature, which inaddition also uses core pins in the mold cavity to assure positivealignment of the previously molded segment. A typical injection mold forplastic material is shown in FIG. 7 at 30, divided into 2 halves. Themold top 31, which seals off the mold cavities 32 at top, is shownseparately for simplicity. The cavities 32 have the configuration tomold a single segment 22, with the cavity 34 at the left end forreceiving the previously molded segment unit 33 next to the previouslymolded trailing end unit 26, the cavity 35 next to the end cavity 34 forreceiving the trailing end unit 26 of the previously molded segment andfor overmolding over the end unit 26 the leading end unit 24 of the nextsegment, and the cavity 36 at the right end for molding the trailing endunit 24 of the next segment. Only the parts 33 and 26 of the previoussegment are shown, the new segment yet to be molded is not shown.

After each molding cycle, still to be described, when the mold halvesare separated, ejector means (not shown) will free the just-moldedsegment, so it can be advanced as shown by the arrow 60. Subgates 38provide passageways for the molten plastic. During the molding process,inert core pins 42, 43 mounted on the top mold part 31 are positioned ineach cavity where a hole 16 is to be formed. The lateral spacing of thecore pins 42, 43 is determined by their mounting in the top core half31.

The end unit 26 has a hole 16 molded into it that is in pitch with allthe other holes 16 in the insulating segment 22 which will in a laterprocess have interconnect devices (pins/socket/etc.) inserted into them.After the first (called previous) discrete segment is molded and cooled,the mold halves are separated and the just-molded segment is ejected andindexed for the next cycle of the mold. After the mold halves areseparated, the discretely molded previous segment is ejected from themold cavity and indexed by a mechanism such as the motor driven gears 44shown to the proper position for the next molding cycle. In thisposition, the unit 33 next to the interlock end unit 26 as well as thelatter are both retained or reinserted in the end cavities 34, 35 of themold. When the mold halves are closed in preparation for the nextmolding cycle, the core pins 42 of the two end-most positions 34, 35 gointo the holes of the unit 33 next to the interlocked units and the endunit 26 into the cavity bottom if a through-hole is to be made. Thisserves to assist in the final location of the previously molded segmentwith relation to the cavity which will mold the next segment. Any minuteerror in the initial location of the previously molded segment iscorrected by the positive positioning provided by the two core pins 42going into the two holes in the two units 33, 26 which remain in themold and whose lateral spacing is fixed by the mold.

The next cycle of the mold fills the cavities with molten plastic, andencapsulates the trailing end unit 26 inside the overmolded part 24 ofthe next segment. The design of the interlock feature is such that theinterlock joint is not the weak joint of the system. This is obtained bymaking the strength of the trailing end and leading units approximatelythe same, so that the combined strength of the overmolded interlockedjoint is approximately the same as that of the middle units, which makesthe notched regions the weakest links in the strip. In a preferredembodiment, substantially equal strength is obtained by a configurationof the trailing end 26, at the cross-sectional area indicated by 70 inFIG. 4B, that is substantially the same as the cross-sectional area atthe smallest section of the web, indicated at 71 in FIG. 4A. In otherwords, even in the molded state (prior to interconnect device insertioninto the insulator), the interlock joint is stronger in tension, bendingand twisting than the webs between the notches 14 that separate eachunit of the discretely molded segment. This is an important feature sothat the process that follows the injection molding, typicallyinterconnect device insertion, can utilize the full range of flexibilityand strength of the discretely molded segments, and not be limited bythe joint at the interlocking units.

A further feature of the invention is that, even though the design issuch that the interlock area is not the weakest link in the strip, afactor of safety is achieved by device insertion. Once a pin or otherelectrical or mechanical part is inserted into the aligned holes 16 thatis the trailing end unit 26 and the over molded material from thesubsequent mold cycle forming the leading end unit 24, the two discretesegments are truly locked together. This is an important featurebecause, even though the interlocking mechanism is designed to bestronger in tension, bending and twisting than the webs of thediscretely molded segments, improper processing conditions or the needfor certain materials which may not fuse together during molding, maylead to the condition where eventually the end unit 26 from the previoussegment can be removed from the encapsulating material 24 of the nextsegment. Once, however, a pin for example, is inserted into the alignedholes 16, the two segments are positively locked together and a higherstrength preventing separation is achieved.

Another benefit of the invention is that, when the molten plastic isinjected into the cavity, it is done so at an extremely high pressure.In the design described in the '622 patent, the protuberance from theprevious segment which extends into the cavity segment will experiencehigh stresses from this high pressure molten plastic. This stress candamage or weaken the protuberance resulting in a weak joint which isundesirable. In the present invention, the inner end unit 26 is not freeto move or flex in the cavity, as it is held tightly in position by thecore pin 42 that goes through the hole in it, thereby securing it inplace. Because the end unit can not move when subjected to the flow ofmolten plastic at such high pressures, it will not be damaged orweakened in the injection molding process, and will retain itsmechanical properties, providing a strong interlocking joint.

The indexing mechanism 44 is easily controlled to advance each previoussegment to the proper position for the core pins 42 to align same forthe next molded segment. The positive alignment provided by the corepins insure proper unit to unit pitch.

FIG. 4 shows at the left the previous segment 22 with trailing end unit26 nesting within the overmolded leading end unit 24 of the next segment22', with their respective holes 16 aligned to received a commonelectrical or mechanical element.

As shown in FIG. 7, as the continuous strip 48 formed of successiveinterlocked molded segments 22 is molded in this step-by-step, indexingprocess, it can be passed through a known inserter machine 50 forinserting pins or other elements into some or all of the holes 16 of thestrip, and then the resultant strip 10 wound up in a continuous fashionon a reel 52 for distribution to a user. From the reel 52, the user at aPCB manufacturing station can unreel the strip 10 either manually orautomatically by machine--shown in FIG. 8 with tab electrical connectors54--and as described sever sections with the desired number of tabs formounting onto a PCB by an inserter machine.

While the more common application of the invention will involveelectrical contacts, such as pins, sockets, tabs, terminals and thelike, for receiving electrical connectors, there are also mechanicalapplications of the invention. One such example can be found in U.S.Pat. No. 5,148,596, (also incorporated herein by reference) which, inthe embodiment disclosed in FIGS. 18-22, describes the insertion ofposts on a PCB to serve as mechanical guides for electrical connectors.Such posts can also be inserted in holes in the continuous molded stripof the invention, and positions containing one or more posts severedfrom the continuous strip for mounting on the PCB. In this instance, theposts need not extend completely through the holes in the strip, aswould normally be preferred for electrical contacts where the portionsprotruding from the bottom can be used for mounting of the header on thePCB, as well as for making additional circuits connections on theopposite side of the PCB. It will also be appreciated from thisapplication that the holes in the strip need not be through-holes, butcan also be blind holes for receiving mechanical or electrical parts.

Similarly, while the more common and preferred arrangement employsevenly spaced through-holes with each hole in both the end and middleunits filled with an electrical contact, there can be users for unevenpatterns of contacts. Thus, holes are not essential in all the units,nor are contacts essential in all the holes. Holes, through or blind,need only be located where needed or to receive a core pin.

Similarly, with a strip of equally spaced holes and contacts, it ispreferred to mold sets of notches separating each contact, allowing anydesired header length to be severed at any of the notched separators.However, if the user has a need for, for example, 3-pin headers, thennotches need only be provided between every third and fourth pin wheresevering will occur. Alternatively, if the user needs both 2-pin and3-pin headers, then the notches need only be provided at 3 and 4 pinpositions, thus where the user intends to sever discrete headercomponents.

It will also be appreciated that other structures capable of weakeningthe strip along discrete lengths thereof, for easy separation of thestrip at the weakened regions, can be substituted for the notches.

The number of units provided in each segment is not critical. It canvary from 3 to more than 50, depending on mold and part size. A typicalvalue would be about 32 units with a pitch of about 0.1 inches, a heightof about 0.1 inches, for 0.025 inch square standard pins, and with a webwidth, between the notches, of about 1/3 the unit width.

As will be observed in FIGS. 3 and 5, the trailing end unit 26 forms akind of knob-shaped in-line protuberance with a recessed or reducedwidth section 60 behind the front axial surface. As a result, materialof the overmolded leading end unit 24 extends into this reduced widthsection which enhances the interlocking of the two segments. As analternative, if the position is not needed by the customer, the core pin42 which engages the hole 16 in the end unit 26 may be omitted. As aresult, injected plastic will fill that hole 16 and provide additionalstrength to the assembly of segments. The remaining core pin 42 willstill function for alignment of adjacent segments. Other core pins 43may also be eliminated if desired.

The use of semi-continuous injection molding offers several advantagesover extrusion. Holes with lead-ins--the bevels 18--may be moldeddirectly. Higher-temperature plastics can be used. Greater dimensionalaccuracy is possible. Pitch is more consistent. The parts are cleanersince no plastic need be removed as is required for extrusion. Alsosecondary machining or punching operations necessary with extrusions areeliminated.

The shape and size of the knob-shaped end 16 is preferably chosen suchthat its strength is approximately the same as the strength of theovermolded plastic that encapsulates the knob-shaped end, so togetherthey provide a strength of plastic substantially equal to that of one ofthe middle units 12, which contributes to the strength of theinterlocking structure thus formed. Substantially equal strength can beobtained by making the volume of the trailing end 16 approximately thesame as the volume of the overmolded plastic. To further ensure that thenotched region represents the weakest link to ensure severing at theproper locations, in a further prepared embodiment, preferably thecross-section of the section 70 shown by hatching in FIG. 4B is equal toor larger than the smallest cross-section 71 through the center of theweb between a pair of notches 14.

The core pins need not be round, as shown. They can also be rectangular,square or otherwise shaped as required for the part to be subsequentlyinserted.

While the invention has been described in conjunction with specificembodiments, it will be evident to those skilled in the art that manyalternatives, modifications and variations will be apparent in light ofthe foregoing description. Accordingly, the invention is intended toembrace all such alternatives, modifications and variations as fallwithin the spirit and scope of the appended claims.

What is claimed is:
 1. A continuous elongated injection-molded length ofinsulating material containing a plurality of spaced approximatelyin-line electrical or mechanical parts inserted in and alongsubstantially the entire length of said insulating material,comprising:(a) a consecutive series of injection-molded segments ofinsulating material, (b) each segment comprising a consecutive series ofconnected integral, insulated units comprised of first leading andsecond trailing end units and a plurality of middle units between theend units, said middle units each being of insulating material andseparated along their length from each other by severance means, somemiddle and end units containing holes for receiving an electrical ormechanical part, the first and second end units forming portions in linewith the spaced electrical or mechanical parts, (c) except for the endsegments, the second end unit of each segment being nested within thefirst end unit of the adjacent segment whereby successive segments areintegrally coupled by their respective second and first end units withtheir respective holes aligned to receive a common electrical ormechanical part, (f) electrical or mechanical pans being mounted intoholes of the middle units and into the aligned holes of the nested endunits of some of the segments.
 2. The product of claim 1, furthercomprising a reel, said elongated length of insulating material withelectrical or mechanical parts being wound up on the reel.
 3. Theproduct of claim 1, wherein the second end unit is generallyknob-shaped.
 4. The product of claim 3, wherein the strength of thesecond end unit is approximately one-half of the combined strength ofthe second end unit and its nested first end unit.
 5. The product ofclaim 3, wherein the volume of the second end unit is approximatelyone-half of the combined volume of the second end unit and its nestedfirst end unit.
 6. The product of claim 1, wherein the severance meansare sets of notches.
 7. The product of claim 6, wherein thecross-section of the second end unit, adjacent the hole, is equal to orgreater than the smallest cross-section of the strip at the notches. 8.The product of claim 4, wherein the electrical or mechanical part is anelectrical contact.
 9. A method of forming a continuous elongatedinjection-molded length of insulating material for receiving a pluralityof spaced approximately in-line electrical or mechanical parts, insertedinto and along substantially the entire length of said insulatingmaterial, comprising the steps:(a) providing a mold shaped to form onesegment of insulating material, said one segment comprising aconsecutive series of connected, integral, insulated units comprised offirst and second end units and a plurality of middle units between theend units, some of the middle and end units containing holes forreceiving an electrical or mechanical part, the first and second endunits forming projecting portions approximately in line with the holesfor receiving the electrical or mechanical parts, (b) introducing intothe mold molten plastic and allowing same to cool to form a firstsegment of insulating material with first and second end units andmiddle units containing holes, (c) removing from the mold the firstsegment and reinserting the second end unit of the first segment in themold, (d) introducing into the mold molten plastic and allowing same tocool to form a second segment with first and second end units and middleunits with the first end unit of the second segment overlapping with thesecond end unit of the first segment whereby the first and secondsegments are integrally coupled by their respective second and first endunits with their respective holes aligned, (e) repeating step (c) withrespect to the second segment and step (d) to form a third segmentintegrally coupled with the second segment, and so on, wherebysuccessive segments can be formed and integrally coupled to form anelongated length of insulating material.
 10. The method of claim 9,further comprising the step of:(f) inserting electrical contacts ormechanical parts into some of the holes of the middle regions.
 11. Themethod of claim 9, further comprising the step of:(f) insertingelectrical contacts or mechanical parts into some of the aligned holesof the overlapping end units.
 12. The method of claim 9, wherein thesecond end unit comprises a generally knob-shaped protuberance generallyin-line with the holes.
 13. The method of claim 12, wherein the strengthof plastic of the second end unit is approximately one-half that of thecombination of the second end unit and the overlapped first end unit.14. The method of claim 12, wherein the volume of plastic of the secondend unit is approximately one-half that of the combination of the secondend unit and the overlapped first end unit.
 15. The method of claim 9,wherein after step (c), and before step (d), a core pin is inserted inthe second end unit reinserted in the mold for maintaining in the secondsegment the same pitch as in the first segment.
 16. A method of forminga continuous elongated injection-molded length of insulating materialcontaining a plurality of spaced in-line electrical contacts insertedthrough and along the entire length of said insulating material,comprising the steps:(a) providing a mold shaped to form one segment ofinsulating material, said one segment comprising a consecutive series ofconnected, integral, insulated units comprised of first leading andsecond trailing end units and a plurality of middle units between theend units, said middle units each being of insulating material andseparated along their length from each other by aligned sets of notches,each middle and end unit containing a hole for receiving an electricalcontact, the first and second end units forming projecting portions inline with the holes for receiving the electrical contacts, (b)introducing into the mold molten plastic and allowing same to cool toform a first segment of insulating material with first leading andsecond trailing end units and middle units each containing a hole, (c)removing from the mold the first segment and reinserting the secondtrailing end unit of the first segment in the mold, (d) introducing intothe mold molten plastic and allowing same to cool to form a secondsegment with first leading and second trailing end units and middleunits with the second trailing end unit of the first segment beingnested within the first leading end unit of the second segment wherebythe first and second segments are integrally coupled by their respectivesecond and first end units with their respective holes aligned toreceive a common electrical contact, (e) repeating step (c) with respectto the second segment and step (d) to form a third segment integrallycoupled with the second segment, and so on, whereby successive segmentscan be formed and integrally coupled to form an elongated length ofnotched insulating material, (f) inserting electrical contacts into eachof the holes of the middle units and into the aligned holes of thenested end units.
 17. The method of claim 16, wherein step (c) iscarried out by ejecting the segment from the mold, indexing the segmentuntil its second trailing end unit remains adjacent the mold, andreinserting the second trailing end unit into the mold.
 18. The methodof claims 17, further comprising inserting a core pin into the hole ofthe trailing end unit reinserted into the mold to align same withrespect to the second segment to be molded.
 19. The method of claim 17,further comprising reinserting in the mold in step (c) the middle unitnext to the second trailing end unit of the first segment.
 20. Themethod of claim 19, wherein a core pin is also inserted in the hole inthe reinserted middle unit to align same with respect to the secondsegment to be molded.
 21. The method of claim 17, further comprising thestep of winding the continuous length onto a reel.